Electrochemical sensors are used to determine the concentrations of various analytes in testing samples such as fluids and dissolved solid materials. For instance, electrochemical sensors have been made for measuring glucose in human blood. Such sensors have been used by diabetics and health care professionals for monitoring blood glucose levels. The sensors are usually used in conjunction with a meter, which measures light reflectance, if the strip is designed for photometric detection of a die, or which measures some electrical property, such as electrical current, if the strip is designed for detection of an electroactive compound.
Typically, electrochemical sensors are manufactured using an electrically insulating base upon which conductive inks such as carbon and silver are printed by screen printing to form conductive electrode tracks or thin strips of metal are unrolled to form the conductive electrode tracks. The electrodes are the sensing elements of the sensor generally referred to as a transducer. The electrodes are covered with a reagent layer comprising a hydrophilic polymer in combination with an oxidoreductase or a dehydrogenase enzyme specific for the analyte. Further, mounted over a portion of the base and the electrodes is an insulating layer.
Precision and accuracy of electrochemical measurements to a great extent rely on the reproducibility of the electrode surface area on a microscopic scale. Variations in the morphology of the electrode can result in very significant changes in the electrochemical signal readout. Screen-printing has made significant in-roads in the production of sensors for determining glucose. The wide use of screen-printing stems from the ability to mass-produce relatively inexpensive sensors. The use of metal strips unrolled from large rolls has also been employed to mass produce such sensors.
While many advances have been made in the field of screen printing and conductive ink production, the technology still suffers from poor reproducibility of the electrode surface area, dimensional variations, thickness variations, micro-cracks, and shrinkage due to the repetitive and high temperature curing processes involved in using film printing technology. Loss of solvent during printing is another factor that leads to variations in the thickness of electrodes.
Sensor development using printing technology requires several passes of different conductive inks demanding different screens. Slight variations in positioning the screens can lead to substantial errors in IR drop and the applied potentials. Wear and tear of these screens is another source of error. Also, sensor strip production by screen printing suffers from a high level of raw material waste. Generally, for every gram of ink used, there is a gram of ink wasted. Manufacture of such sensors also involves several lamination processes that add to the production complexity and cost of the final product.